The present application relates to systems and integrated circuits which include multiple independently powered-up “power islands” inside a single integrated circuit.
Many portable electronic systems are critically limited by battery life. For example, users do not like heavy cell phones, but users also do not like their cell phones to run out of power and shut down. One way to improve battery life is to increase the energy efficiency of the electronics components in the portable system.
As the constraints of low-power integrated circuits have steadily become tighter, the technique of power islands has become more important. In this technology some portions of an integrated circuit are powered up only on an “as-needed” basis. Some implementations have used variable clock frequency for individual power islands, see e.g. U.S. Pat. No. 7,051,306, which is hereby incorporated by reference in its entirety. Some implementations have selectable supply voltage levels for individual power islands, see e.g. U.S. Pat. No. 7,080,341, which is also hereby incorporated by reference in its entirety. Some implementations even use “smart” supply voltage switching, where the timing of supply switching to power islands is fine-tuned to avoid out-of bounds transients: see e.g. US 2006/0190744, which is also hereby incorporated by reference in its entirety.
It should be noted that power islands technology is very different from smart power technology. See e.g. Smart Power ICs (2.ed. Murari et al. 1995). In smart power technology logic or mixed-signal stages, operating at normal supply voltages, are combined in the same chip with higher-voltage driver circuits. Special device structures, which would not be used in a pure logic or mixed-signal chip, are commonly used to permit use of both high-voltage and low-voltage areas.
The use of on-chip power islands has many advantages for reducing power consumption, but the inventors have realized that there are also some surprising difficulties, which are addressed by the various inventions described in the present application. Some of the points of invention will now be described, followed by additional explanation of the benefits of those points.